1. Field of the Invention
The present invention concerns a high pressure fluid supply pipe used in pipelines for supplying high pressure fluid such as fuel supply pipes for diesel internal combustion engines or hydraulic pipelines for hydraulic apparatus and, more in particular, it relates to a method of manufacturing a high pressure fluid supply pipe having resistivity to high inner pressure, in particular, capable of remarkably improving the wear resistance to repeated inner pressure by providing a compressive residual stress to the inner surface of the pipe.
2. Description of the Prior Art
For manufacturing high pressure pipelines for supplying a high pressure fluid such as fuel supply pipes in diesel internal combustion engines or supply pipes for hydraulic oils in hydraulic apparatus, products of a required size have been obtained by reducing the diameter of a carbon steel pipe defined as a carbon steel pipe for high pressure pipelines in JIS G 3455 (STS steel pipe) into a required pipe diameter by means of cold drawing. However, since the thus manufactured pipe is poor in the strength for high inner pressure, in particular, in the fatigue resistance against repeated high pressure, it has been adopted such a means of increasing the pressure resistant strength by replacing STS 38 steel pipes with STS 42 steel pipes or replacing STS steel pipes with SUS steel pipes having higher yielding point and tensile strength, or improving the strength only near the inner circumferential surface by means of soft gas nitrization or carburization since the stress caused by the inner pressure of the pipe reaches maximum at the inner surface.
However, since means for replacing the pipe material with that of higher strength increases the yielding point and the tensile strength of the entire pipe, it involves a problem that the bending fabrication for forming a shape of a product is difficult and, further, the material cost is increased. On the other hand, means of strengthening the inner surface requires an expensive cost for the treatment of the inner surface of the pipe, as well as it hardens to embrittle the inner surface of the pipe making it inappropriate for the molding fabrication after the strengthening treatment for the inner surface. Thus, it requires a strengthening treatment for the inner surface after shaping into a predetermined shape as a product. In this treatment, deformation is caused due to the high temperature treatment and it is difficult to recover a correct original shape, which brings about excessive stresses upon mounting to a place for use such as in an internal combustion engine to possibly cause cracks in the hardened layer.